Method and system for connecting plate-like members of bipolar plates

Abstract

The invention relates to a method for joining plate-like components of bipolar plates, comprising the steps of placing a first plate-like component on a clamping surface, placing a second plate-like component on the first plate-like component, applying a plurality of pressing devices on the outer surface of the second plate-like component, which faces away from the first plate-like component and the clamping surface, wherein a provided gap extension remains exposed between the pressing devices, pressing the plate-like components together by all pressing devices, wherein for this purpose a magnetic force acting in the direction of the clamping surface is applied to at least one of the pressing devices, and welding the plate-like components in an uninterrupted working process along the gap extension.

Description

TECHNICAL FIELD

[0001] The invention relates to a method and a system for joining plate-like components of bipolar plates. BACKGROUND

[0002] Fuel cell systems usually have a stack of a plurality of fuel cells in which an electrochemical process between oxygen and hydrogen is operated with the provision of electrical power. Here, the individual fuel cell is essentially composed of a membrane electrode assembly which is surrounded by bipolar plates. Such a membrane electrode assembly has, for example, fine flow channels (so-called "flow fields") on the surfaces opposite to each other for the supply of reactants (Edukten) and the discharge of reaction products. The bipolar plates can be composed of an anode sheet metal and a cathode sheet metal which are welded to each other and enable the internal guiding of a cooling medium. The material thickness of the sheet metal, which is usually made of steel, can be one-tenth of a millimeter or less.

[0003] The welding can be carried out by means of laser beam welding. In order to achieve a small misalignment, the process parameters for the welding method are chosen in such a way that as small an energy input as possible is achieved. This results in a very narrow weld seam, the weld seam width of which is usually only one-tenth of a millimeter or less in the case of small pool volumes. Overall, this results in poor gap bridging in combination with the high process speed required thereby, so that a gap of 30-50 μιη between the sheet metals already leads to defects and thus to leaks in the bipolar plate.

[0004] Since the welding process is very sensitive with regard to the presence of a component gap, a pressing device is used for producing a technical zero gap in the region of the joint. Due to the tolerances of the anode sheet metal and the cathode sheet metal, it is necessary to press the sheet metals on both sides of the weld seam to be produced. In the case of bipolar plates, closed welding tracks are produced for ensuring a closed sealing profile. For this purpose, the welding masks are placed successively on the sheet metals to be joined in several steps and press the part of the profile respectively. The welding track thus comprises a plurality of individual weld seams with a starting point and an end point and their overlap, which ultimately results in a closed weld seam. In comparison with a constant operating process, this can result in a process instability and an increased susceptibility to errors. SUMMARY

[0005] It is the task of the invention to provide a method and / or a system for joining plate-like components of bipolar plates which prevents the above-mentioned disadvantages and which enables, in particular, a completely closed welding track.

[0006] A method for joining plate-like components of bipolar plates is proposed, comprising the following steps: placing a first plate-like component on a clamping surface, placing a second plate-like component on the first plate-like component, applying a plurality of pressing devices on the second plate-like component on the side facing away from the first plate-like component and the clamping surface, wherein a provided seam extension is kept exposed between the pressing devices, pressing the plate-like components together by all pressing devices, wherein for this purpose a magnetic force acting in the direction of the clamping surface is applied to at least one of the pressing devices, and welding the plate-like components in an uninterrupted working process along the seam extension.

[0007] As mentioned above, the two plate-like components can comprise an anode plate and a cathode plate. The anode plate and the cathode plate are preferably embodied as steel plates and have a material thickness of preferably significantly less than one millimeter, about one tenth of a millimeter or less. A first plate-like component, which can be an anode plate or a cathode plate, is placed first onto the clamping surface. The flow field formed on the first plate-like component is pressed here and directed towards the clamping surface. Subsequently, a second plate-like component is placed onto the first plate-like component, wherein here the flow field of the second plate-like component is directed away from the clamping surface. The two plate-like components are connected to each other in this arrangement.

[0008] In order to form a zero gap in the provided seam extension, a plurality of pressing devices is used. These are configured for pressing the second plate-like component onto the first plate-like component such that a flush contact between the two plate-like components is established in the provided seam extension. Here, all pressing devices are pressed onto the second plate-like component simultaneously instead of being placed one after the other as is customary. By using a magnetic force acting on at least one of the pressing devices, it is also possible to enclose the closed seam extension on both sides without restricting the accessibility of the welding device from the outside of the second plate-like component. The application of the magnetic force can be achieved by a magnetic unit, for example by a permanent magnet or a selectively activatable electromagnet. The at least one pressing device to which the magnetic force is applied can also comprise a permanent magnet, an electromagnet or a body made of a magnetic material. Since all pressing devices are used simultaneously to press the plate-like components together, a completely exposed closed seam extension can be defined. In particular, the pressing device or the plurality of pressing devices can be loaded with a magnetic force, provided that these would need to be mechanically articulated due to their position on the seam extension, which would constitute an obstacle to the welding device.

[0009] This leads to a significant improvement in the weld properties that can thus be achieved for bipolar plates, since defects, local leaks and thus rejects can be reliably and reproducibly reduced. Since the number of working steps and the total length of the weld are reduced, the costs for manufacturing bipolar plates can be further reduced.

[0010] In an advantageous embodiment, the welding comprises laser welding. It is for example conceivable to use a laser or a carbon dioxide laser (Nd:YAG or CO2 laser). These types of lasers can achieve very narrow weld seams and small volumes of the molten bath by suitable process control. In particular, Nd:YAG lasers can be focused very precisely and produce particularly fine weld seams.

[0011] As mentioned above, the seam extension preferably comprises a circumferential track. The weld seam can be produced without interruption in a single work process along the seam extension, since there are no obstacles along the seam extension and thus the disadvantages of the prior art are overcome with the use of the at least one magnetic supporting press.

[0012] In the method according to the application, the application of the press can also comprise arranging at least one inner press within the seam extension and at least one press outside the seam extension, wherein a magnetic force is applied to the at least one inner press. The press arranged within the seam extension, i.e. inside the edge of the arranged seam extension, does not require any further mechanical means to perform the fixation of the press. Thus, no mechanical means protruding beyond the seam extension are required, which would hinder the welding device. Only one, in particular inner, press can be sufficient as long as a zero gap can be ensured.

[0013] Here, a system for joining plate-like components of bipolar plates is proposed, comprising a clamping plate having a clamping surface, a plurality of presses for pressing two plate-like components together on the clamping surface, at least one magnetic unit and a welding device, wherein the at least one magnetic unit is arranged on the side of the clamping surface facing away from the presses, wherein the at least one magnetic unit is configured to apply a magnetic force to at least one of the presses such that the associated at least one press is pressed against the clamping surface, wherein the presses are shaped to keep the arranged seam extension exposed between the presses in a state pressed onto the plate-like components, and wherein the welding device is configured to weld the plate-like components along the seam extension.

[0014] The clamping plate can have a flat surface onto which one of the plate-like components can be placed directly. This surface, also referred to as clamping surface, can also have grooves, protrusions, recesses or other features that can engage with the geometry of the first plate-like component. In the case of plate-like components embodied as thin plates, the thin plates form flow fields on their outer sides, respectively, so that flow channels of the flow fields can be used for precisely positioning the first plate-like component on the clamping surface.

[0015] The at least one magnetic unit can have at least one permanent magnet and / or at least one electromagnet. The magnetic unit can be arranged below the clamping plate or at least partially in the clamping plate, wherein the magnetic field lines must be able to extend through the clamping plate and the plate-like component located thereon. The at least one magnetic unit can attract the one or more pressing devices in the direction of the clamping surface, such that the plate-like component placed thereon is pressed together at the edge side of the provided slit extension. A flush contact as described above can thus be achieved at the provided slit extension.

[0016] In an advantageous embodiment, the pressing device has at least one outer pressing device and at least one inner pressing device, wherein the at least one inner pressing device is shaped for surrounding the slit extension relative to the at least one outer pressing device. The at least one inner pressing device is completely surrounded by the closed slit extension. The inner pressing device can be placed inside the edge of the slit extension. The outer pressing device, however, is placed simultaneously outside the edge of the slit extension. These pressing devices can also be held by means of conventional mechanical mechanisms, such as pressing tools, clamps, levers, actuating elements, etc., instead of by means of the magnetic unit, since these pressing devices do not cover the provided slit extension.

[0017] In an advantageous embodiment, the at least one inner pressing device comprises at least two sections which are mechanically coupled to one another. The sections form separate pressing device bodies which are coupled to one another by mechanical means. The coupling can be achieved, for example, by means of a shape-elastic connection, such as a compression spring or a tension spring. The division into sections allows a more elastic bearing onto the plate-like component to be achieved. In order to ensure zero play over the entire slit extension, large pressing forces are sometimes required, in the case of which the plate-like component is locally deformed. The divided sections are particularly suitable for avoiding a locally only point-like bearing. The coupling between the sections, however, enables a lateral orientation of the sections relative to one another.

[0018] It is particularly preferred that the at least one inner pressing device comprises at least two sections which are mechanically independent of one another. The orientation of the sections can be achieved by means of separate guide devices or by means of shape features of a second plate-like component. It cannot be ruled out that the inner pressing device has not only mechanically coupled sections but also independent sections.

[0019] For the orientation, the at least one pressing device can comprise at least one protrusion for embedding into a recess of the plate-like component. The recess can be achieved, for example, by means of a flow channel of a flow field, into which a matingly shaped recess can be embedded and determines the lateral position of the associated pressing device.

[0020] In a preferred embodiment, at least one of the pressing devices is inclined in the region adjacent to the provided seam extension in a direction away from the seam extension. Thus, more space can be provided for the welding device to realize the seam extension.

[0021] In a particularly advantageous embodiment, the magnetic unit comprises at least one electromagnet. The electromagnet can be activated after placing the plate-like component and switched off after the end of the welding process, which significantly facilitates the handling of the component. Furthermore, the electromagnet can also be part of a conveying unit in a flow production, in which a plurality of bipolar plates are manufactured successively and sequentially. BRIEF DESCRIPTION OF DRAWINGS

[0022] Further measures to improve the application are shown in more detail below on the basis of the drawings in connection with a description of preferred embodiments of the application.

[0023] The drawings show:

[0024] Figure 1 : schematic view of the system in cross section;

[0025] Figure 2 : top view of the system;

[0026] Figures 3 to 5 : system with segmented inner pressing device;

[0027] Figure 6a and 6b : different flow fields on the plate-like component;

[0028] Figures 7 to 10 : detail section view of the system;

[0029] Figure 11 : modification of the system for flow production

[0030] Figure 12 : schematic block diagram of the method. DETAILED DESCRIPTION

[0031] Figure 1A system 2 for connecting two plate-like members 4 and 6 of bipolar plates is shown. The system 2 comprises for this purpose a clamping plate 8 with a clamping surface 10. Furthermore, a plurality of pressing devices 12, 14 and 16 are provided for pressing the two plate-like members 4 and 6 together on the clamping surface 10. The lateral outer pressing devices 12 and 16 shown in the drawing plane can also be pressed against the clamping plate 8 by mechanical pressing or holding devices, while the inner pressing device 14 is pressed in the direction of the clamping plate 8 by magnetic force. For this purpose, a magnetic unit 18 is arranged below the clamping plate 8. If the pressing devices 12, 14 and 16 are at least partially composed of a magnetic material, these are attracted by the magnetic unit 18. Here, these are pressed with support sections 20 onto the plate-like members 4 and 6, respectively. A slot extension 22 provided is fixed on both sides tightly surrounded, so that a locally planar contact exists between the two plate-like members 4 and 6. A welding device 24, which is embodied for example as a laser welding device, which emits a laser beam 26, can weld the two plate-like members 4 and 6 along the slot extension 22.

[0032] In order to follow the arbitrarily shaped slot extension 22, the welding device 24 can be moved for example in rotation and / or in translation along two axes. In order to sufficiently keep the slot extension 22 free, the lateral edges 28 of the pressing devices 12, 14 and 16 are for example inclined in the direction away from the slot extension 22. In order to avoid welding of the plate-like members 4 and 6 to the clamping plate 8, a recess 30 is also provided below the provided slot extension 22.

[0033] In Figure 2 , the system 2 is shown in a top view. Here, the two lateral pressing devices 12 and 16 are shown as elongated members parallel to each other and spaced apart from each other. These two lateral pressing devices can be supplemented by additional pressing devices 32 and 34 extending perpendicular thereto, which are also arranged parallel to each other and spaced apart from each other. The inner pressing device 14 is provided in the form of a rounded rectangle. The pressing devices 12, 14, 16, 32 and 34 surround the provided slot extension 22, which also has a rounded rectangular shape exemplarily.

[0034] In Figure 3 , a variant is shown in which the inner pressing device 14 is divided into a plurality of sections 36 and 40. The two sections 36 on the left in the drawing plane are coupled to each other mechanically by coupling springs 38, respectively. The coupling springs can be compression springs or tension springs, which are configured for pressing into a predefined neutral position. The two sections 40 on the right in the drawing plane are independent of the other sections 36 and are also not connected to the other sections. These two sections can thus be guided for example via a guide geometry arranged in the second plate-like member 6 or configured in the second plate-like member 6 by a flow field arranged on the second plate-like member.

[0035] InFigure 4 Another modified variant is shown, in which multiple segments 36 and 40 are provided, implemented either mechanically coupled or independently. Segments 36 and 40 each have a groove 42 through which the welding device 24 shown above can perform spot welding, for example, in the form of each stepplate. This improves shape stability, especially for larger bipolar plates. Figure 5 Sections BB and CC are marked in the middle. Figure 7 and 8 The diagram shows sectional views, in which the quilting and orientation are seen more clearly.

[0036] Figure 6a and 6b Flow fields 44 and 46 are shown respectively, and these flow fields have flow channels 48 for supplying reactants and discharging reaction products. Figure 6a The flow field 44 shown has flow channels 48 extending in directions perpendicular to each other. Therefore, the flow field 44 is a cross-flow field. Conversely, Figure 6b The flow field 46 includes flow channels 48 with only parallel extensions, making this flow field a “counter-flow”. If segment 40 is applied to either flow field 44 or 46, the shape features of the flow channels 48 can be used for orientation. Figure 6a The flow field 44 can achieve simple orientation in two spatial directions, which is easily achieved in only one spatial direction in the flow field 46. However, if a single flow channel 48 has locally different heights, then a shape feature can be achieved at which precise orientation in two spatial directions can be achieved.

[0037] Figure 7 The cross-section BB is shown. There you can see a transverse clamping device with a groove 42, through which the laser beam 26 can produce the quilting 50.

[0038] exist Figure 8 The diagram shows a clamping device having a plurality of protrusions 52 and 54 that engage with and are oriented into the grooves 56 of the first plate-like member 6. Here, the protrusions 52 are sized such that, although they extend into the grooves 56, they do not contact the second plate-like member 6. This occurs only at the protrusions 54, so that a defined surface contact is only created there.

[0039] exist Figure 9The inner pressing device 14 is shown centered on the side face 58 of the second plate-like member 6 with the bearing section 20. Thereby, the inner pressing device 14 can be placed exactly onto the second plate-like member and thus arranged inside the edge of the provided slit extension 22.

[0040] Figure 10 The inner pressing device 14 is shown with a protrusion 59, the cross section of which is rounded on its outer end and embedded in a rounded recess 60 of the second plate-like member 6. With the rounded shape a simple self-centering is achieved and sometimes a tilting when bearing the inner pressing device 14 can be prevented.

[0041] Figure 11 A possible extension is shown in the form of a continuous system 62 for the production of bipolar plates in series. Here, a plurality of clamping plates 8 are guided continuously on a first conveying unit 64. Along an effective path 66, the clamping plates 8 can be equipped with the supplied plate-like members 4 and 6 (see I) (see II). Subsequently, a pressing device 74 is supplied (III) and bears (IV) on the plate-like members 4 and 6. A magnetic force is exerted on the pressing device 74 (V), after which the two plate-like members 4 and 6 are welded (VI). Subsequently, the pressing device 74 is removed again (VII) so that the resulting bipolar plate 68 (VIII) can be removed (IX). The pressing device 74 can be transported by a second conveying unit 70, which can also transport and place additional magnetic pressing plates 72, which can also be used to transport the pressing device 74.

[0042] Figure 12 Finally, a schematic representation of the method according to the application is shown. The following steps are carried out here: placing 76 a first plate-like member 4 on a clamping surface 10, placing 78 a second plate-like member 6 onto the first plate-like member 4, applying 80 a plurality of pressing devices to the second plate-like member 6 on the side facing away from the first plate-like member 4 and the clamping surface 10, wherein the provided slit extension 22 remains exposed between the pressing devices. Subsequently, the plate-like members 4, 6 are pressed together 82 by all pressing devices, wherein for this purpose a magnetic force acting in the direction of the clamping surface 10 is applied 84 to at least one of the pressing devices. Finally, the plate-like members 4, 6 are welded 86 along the slit extension 22 in an uninterrupted working process.

Claims

1. A method for connecting plate-shaped members (4, 6) of bipolar plates, comprising the following steps: - Place the first plate-shaped member (4) (76) on the clamping surface (10), - Place (78) the second plate-shaped member (6) onto the first plate-shaped member (4). - A plurality of clamping devices (12, 14, 16, 32, 34, 74) are applied (80) to the second plate-shaped member (6) on a side opposite to the first plate-shaped member (4) and the clamping surface (10), wherein the provided slit extensions (22) are kept exposed between the clamping devices (12, 14, 16, 32, 34, 74), wherein the clamping devices (12, 14, 16, 32, 34, 74) are at least partially made of magnetic material. - The plate-shaped members (4, 6) are pressed together (82) by all the clamping devices (12, 14, 16, 32, 34, 74), wherein, for this purpose, a magnetic force acting in the direction of the clamping surface (10) is applied to at least one of the clamping devices (12, 14, 16, 32, 34, 74), and - The plate-shaped members (4, 6) are welded (86) along the seam extension (22) in an uninterrupted working process, wherein the application (80) of the clamping devices (12, 14, 16, 32, 34, 74) includes arranging at least one inner clamping device (14) within the seam extension (22) and at least one outer clamping device (12, 16, 32, 34, 74) outside the seam extension (22), and wherein magnetic force is applied to the at least one inner clamping device (14).

2. The method according to claim 1, characterized in that, The welding (86) includes laser welding.

3. A system (2, 62) for connecting a plate-like member (4, 6) of a bipolar plate according to the method of claim 1 or 2, comprising: - A clamping plate (8) having a clamping surface (10), - Multiple clamping devices (12, 14, 16, 32, 34, 74) are used to press two plate-shaped members (4, 6) together on the clamping surface (10). -At least one magnetic unit (18), and - Welding device (24), The at least one magnetic unit (18) is arranged on the side of the clamping surface (10) facing away from the clamping device (12, 14, 16, 32, 34, 74). The at least one magnetic unit (18) is configured to apply magnetic force to at least one of the clamping devices (12, 14, 16, 32, 34, 74), such that the at least one clamping device (12, 14, 16, 32, 34, 74) presses against the clamping surface (10). The clamping devices (12, 14, 16, 32, 34, 74) are configured to maintain the provided slit extension (22) exposed when pressed against the plate-like members (4, 6) between the clamping devices (12, 14, 16, 32, 34, 74). The welding device (24) is configured to weld the plate-shaped members (4, 6) along the seam extension (22).

4. The system (2, 62) according to claim 3, in, The at least one inner clamping device (14) is shaped to surround the seam extension (22) relative to the at least one outer clamping device (12, 16, 32, 34, 74).

5. The system (2, 62) according to claim 3 or 4, in, The at least one internal clamping device (14) includes at least two mechanically coupled sections (36).

6. The system (2, 62) according to claim 3 or 4, in, The at least one internal clamping device (14) comprises at least two mechanically independent sections (40).

7. The system (2, 62) according to claim 3 or 4, in, The at least one clamping device (12, 14, 16, 32, 34, 74) includes at least one protrusion (52, 54) for embedding into a groove (56) of the plate-like member (4, 6).

8. The system (2, 62) according to claim 3 or 4, wherein, At least one of the clamping devices (12, 14, 16, 32, 34, 74) is inclined in a direction away from the seam extension (22) in the area adjacent to the provided seam extension (22).

9. The system (2, 62) according to claim 3 or 4, in, The magnetic unit (18) includes at least one electromagnet.

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